Foster, a three-time Pro Bowl running back, has 4,521 rushing yards and 44 rushing touchdowns over the past four seasons. Houston has finished 10-6 and 12-4, respectively, over the past two years. The Texans recorded playoff victories each of the last two seasons riding Foster and a strong running game.

The Texans need to hope that's not a thing of the past already.

Foster continues to deal with back soreness, which is now causing problems with his legs, and Kubiak told the Houston Chronicle he was unsure when his running back will return, saying the trainers want to give it a few more days "or whatever that period of time is" before Foster returns to the field.

“He has some lower-back soreness that’s bothering him in his legs a little,” Kubiak said. “He’s had some injections to try and alleviate some of the soreness.

“The way I understand it right now, we’re trying to get through the injection process, that it’s causing some discomfort, and it’s something that’s going to take some time for him to get through.”

Kubiak also expressed concern about the lack of depth behind Foster. Texans running back Ben Tate started in two of the 15 games he appeared in as a rookie and finished with 942 rushing yards and four touchdowns that year. He also appeared in 11 games last season. But once you get past Tate, Houston’s unproven backfield features Deji Karim, plus rookies Cierre Wood and Dennis Johnson.

However, Kubiak’s biggest worry should be why Foster’s body is breaking down at only 26 years old.

Foster began training camp on the physically unable to perform (PUP) list due to a lingering calf injury. He is now fighting a back injury with the regular season less than three weeks away.

The easiest explanation is Foster’s workload the past few years. Foster had 327 carries in 2010 (third in the NFL), 278 in 2011 (sixth in the NFL), and a whopping 351 carries last season (leading the NFL). Foster's 956 regular-season carries from 2010-2012 is not only first in the NFL, it's 99 more than former Falcons running back Michael Turner, who is second on the list – and out of the NFL at the moment.

Foster has dabbled with a vegan diet before (he has since said he fell off the wagon), which has led many to question if his body obtains sufficient nutrition to deal with the constant pounding of the NFL. It could be a case of bad luck, or a combination of several aforementioned factors.

Regardless of the reason, there are still too many unanswered questions surrounding Foster with the start of the season coming soon.